The armoring of vehicles usually requires that plates are held together and/or in place by some form of mechanical fastener or welding. Ballistic protection is enhanced either by overlapping the armor plates or by covering over joints with additional plates. In most cases the armor materials are parasitic and do not add any significant strength to the vehicle.
The high overpressures and shock waves produced by the explosives cause the plates to exert a great amount of force on the mechanical fasteners and/or welds. As a result, pieces of armor can become dislodged and become shrapnel as well. Often the armor will fail at the site of a pre-formed hole or a weld. The net effect of non-directional explosive attack on most current armor systems is to dislodge the armor and significantly alter the structure of the vehicle to the point that it is no longer continuous.
As indicated above, a particular problem associated with joined armor plates is that the failure tends to occur at the joint. Once a crack is initiated, it tends to propagate, and often results in catastrophic failure of the entire plate.